1. Field of the Invention
The present invention relates to a complementary semiconductor device using a metal gate electrode and a high-dielectric-constant (high-k) gate insulating film, and to a method of manufacturing the same.
2. Description of the Related Art
Slimming of a gate insulating film is required for device scale reduction to realize high performance of an LSI. In order to meet the foregoing requirements, the following studies have been made. Specifically, a so-called high-k insulating film having a dielectric constant higher than SiO2 is used as the gate insulating film. A metal gate electrode eliminating a depletion layer peculiar to a polysilicon electrode is used as a gate electrode. The foregoing new materials are able to slim an effective gate insulating. In this way, it is expected to realize a low power consumption device having a leakage current lower than SiO2.
The following condition is a premise of selecting a metal gate electrode material. Namely, in order to reduce power consumption, the metal gate electrode shows a work function for applying a proper threshold voltage at an interface with a gate insulating film in both n- and p-MOS transistors. Specifically, in the n-MOS transistor, the metal gate electrode preferably has a work function of about 4.1 eV close to energy of a silicon conduction band. In the p-MOS transistor, the metal gate electrode preferably has a work function of about 5.2 eV close to energy of a silicon valence band.
However, when different metal materials are used as the gate electrode each of n- and p-MOS transistors, the manufacturing process is extremely troublesome, and thus, this is a factor of causing an increase of the manufacturing cost. Under the present circumstances, there is not still found a metal material for each of the metal gate electrodes for n- and p-MOS transistors, that is, the metal material which has a tolerance to LSI manufacture process such as heat treatment for activating a source/drain region and shows the foregoing work functions. More specifically, there is the following tendency (e.g., see JP-A 2006-222385 (KOKAI)). According to the tendency, a gate electrode material used for the n-MOS transistor has a work function more than an ideal value; conversely, a gate electrode material used for the p-MOS transistor has a work function lower than the ideal value. As a result, the threshold voltage of each transistor becomes high.
In view of the foregoing circumstances, it is desired to realize a complementary semiconductor device, which can obtain a proper threshold voltage in both n- and p-MIS transistors using a metal gate electrode and a high-dielectric-constant gate insulating film, and a method of manufacturing the same.